Measles, MMR vaccine
To date no microbe has been identified as the cause of CD. The bacteria living in the intestine are very numerous (10¹² per gram of faeces) and there are hundreds of different strains and species. Only two-thirds of these have been fully identified and it is still possible that something that causes CD or UC may yet be discovered. What is clear is that the normal balance of healthy bacteria is upset in IBD with both a reduction in lactobacilli and bifidobacteria and an increase in organisms which are normally oxygen loving but somehow manage to survive in the colon where oxygen is in short supply (facultative anaerobes). The possibility that this changes the normal breakdown of the intestinal contents and that this leads to disease is currently being investigated.

1. Measles, MMR vaccine
The measles virus and MMR vaccine have recently been the subject of intense media coverage reporting a link with the development of Crohn's disease. This has caused much concern and anxiety amongst sufferers of the disease and their families.

On the 23rd of March 1998 the chief medical officer, Sir Liam Donaldson, from the Department of Health, together with a group of experts, met to review all recent works and some, as yet unpublished data on the subject. Some of the issues considered included:

1. A Swedish study showed that 3 out of 4 children born to mothers exposed to the virus in late pregnancy went on to develop Crohn's disease. However, two larger controlled studies from England and Denmark showed no increased risk of Crohn's disease under the same circumstances.

2. A comparison of a cohort of children immunised in 1964 with unimmunised children in 1958 suggested an increased risk of Crohn's disease in the immunised group.

However, a second study, which was more reliable as it used appropriately matched controls, and similar studies in Oxford and Finland showed no increase in Crohn's disease following the introduction of the measles or MMR vaccine

3. Workers at the Royal Free Hospital in London have claimed to demonstrate the presence of the virus in tissues of patients with Crohn's disease. However, an independent group, using identical methods could not reproduce these results. Three groups, including the Royal Free Hospital, using the most sensitive and specific techniques, failed to detect measles virus genetic material in either tissues affected by Crohn's disease, normal bowel tissue, or in peripheral blood lymphocytes of Crohn's sufferers.

If measles viruses were present they would have been detected by these methods. In addition, measles specific antibodies do not appear to be raised in individuals with Crohn's disease.

After careful consideration of the material available, together with the opinions of the experts, the following conclusions were made:

• There is no support of a causal role for persistent measles virus infection in Crohn's disease.

• There is no link between the MMR vaccination and bowel disease

• There is therefore no reason for change in the current MMR vaccination policy and that giving the vaccines separately would leave children and their contacts unnecessarily exposed to preventable infectious diseases along with their often serious consequences.

We regret that we cannot make the decision as to whether you should or should not have your child immunised with the MMR vaccine. This decision has to be yours based on the available evidence and the support of the medical team delivering your care.

Further information and support groups available to help you with your decision include: NACC, 4 Beaumont House, Sutton Road, St Albans, Herts. AL1 5HH.
Tel: 01727 844296 www.nacc.org.uk
The Department of Health. www.doh.gov.uk

2. Mycobacterium paratuberculosis
As a sufferer from Crohn's disease you may be concerned following the recent publication in the national press implicating mycobacterium paratuberculosis as a cause of the disease.

The organism is known to cause a similar disease in animals, (Johne's disease) and for many years workers have been trying to link it to the development of Crohn's disease in humans, with varying degrees of success.

Professor Hermon Taylor and his colleagues at St George's Hospital in London reported to have found mycobacterium paratuberculosis in about 65% of their Crohn's disease patients. Tissue samples were taken from operation specimens and DNA isolated using sensitive testing methods. However, Rowbotham and his colleagues at St James's Hospital in Leeds were unable to reproduce these positive results despite using the same testing methods and other more specific and sensitive methods. the reasons for the positive findings were thought to be due to laboratory contaminants or other artefacts of testing.

The organism can occur in milk supplies (unpasteurised), tap water and soil and it is likely that mycobacterium paratuberculosis is a secondary invader which may influence histological changes but is not the primary cause of the disease.

For a disease to be infectious it must satisfy the four postulates of the great bacteriologist Robert Koch, i.e.

1. The organism must be present in all cases of the disease
2. It must be isolated and grown in pure culture
3. It must reproduce the disease in a suitable experimental animal
4. It must be transmitted to another animal and be recovered from the animal in which it has caused the disease

Professor Taylor was only able to find the organism in 65% of his patients; other workers were unable to isolate a single organism except in one non-Crohn's patient. Therefore these postulates are not satisfied.

It is extremely rare for Crohn's disease to occur in the spouse of a patients. First degree relatives not living together have a very much higher incidence of the disease, suggesting a genetic, rather than infectious link.

Lastly, treatment with anti-tubercular therapy is ineffective in the treatment of Crohn's disease.

Although gastroenterologists may talk about bacteria being a possible cause of the disease, this is not due to infection, but rather to the process of abnormal fermentation of food residues in the large intestine. Chemicals are produced from this process which may damage the lining of the intestines causing inflammation, ulceration and bleeding.

It is possible that you may be intolerant to the protein or sugar in milk which can lead to the development of the disease when these products are fermented and not due to the fact that the milk could be contaminated with mycobacterium paratuberculosis.

If you have further concerns or doubts about the safety of milk you could always switch to ultra heat treated milk (UHT) or discuss the matter further with the doctor.

3. Faecalobacterium prausnitzii (Fp)
Recently there has been considerable excitement because a French group of workers reported that patients with CD had low numbers of this organism living in their intestines. Fp has an anti-inflammatory effect and it was suggested that inflammation in the bowel was therefore allowed to develop raising hopes that it might be possible to treat CD by giving sufferers this bacterium. Unfortunately we found no difference in the numbers of Fp in patients with CD, UC irritable bowel syndrome and healthy controls. Furthermore when patients with CD were treated successfully by elemental diet the numbers of Fp, far from increasing, became even lower. If a reduction in numbers is associated with improvement in CD it is difficult to see that lack of Fp can be an important factor in producing this disease.

4. Sulphate reducing bacteria (SRBs)
These bacteria live in the bowel and produce hydrogen sulphide (H2S) which is a very toxic chemical. It has therefore been suggested SRBs may be important in causing IBD. This suggestion has still to be proved. It seems likely that H2S is rapidly reconverted to sulphate, which is harmless, making it unlikely to be important.

5. Yersinia
Yersina is an organism which may infect the small intestine giving changes which are similar to those of CD. However, there is no evidence to date to suggest that this is the cause of the disease.